The role of macromolecules is pervasive in the manufacture and fabrication of a wide variety of articles. Plastics, synthetic fibers, elastomers and innumerable other products are derived from polymers. A great deal of effort and attention has been funnelled into polymerization processes, i.e. the preparation of polymers. Much effort has also gone into the preparation of useful articles from polymers once they have been prepared. Such polymer processing techniques commonly involve molten processing of the polymers. Such molten processing technology includes molding, extrusion, compounding, spinning, spraying and other procedures.
A persistent problem remains in the fabrication of useful articles from polymers because of the unique rheological and mechanical properties of polymers. On the one hand, high molecular weights are generally desirable from the consideration of the mechanical properties of the article ultimately formed therefrom; on the other hand, however, higher molecular weights tend to make processing and fabrication from the melt more difficult. In the molten state, polymer chains can move freely, though often with enormous viscosity, past one another if a sufficient force is applied. The fabrication of most polymeric articles utilizes this principle, and this is the chief example of the plasticity from which the very name "plastics" is derived.
The melt viscosity of polymers in hot melt pressure sensitive adhesives (HMPSA's) applied by spraying is particularly troublesome. In order to be sprayable, the polymer must have a desirably low melt viscosity at high shear encountered during spraying the adhesive through a small orifice. On the other hand, the polymer desirably has a high melt viscosity at a low or non-shear condition in order to minimize spreading and creeping of the adhesive after it is applied to a substrate surface by spraying, but before it has cooled sufficiently to solidify. The adhesive must, of course, also have adhesive properties to serve as an adhesive, and cannot severely degrade at spraying conditions (i.e., under shear at high temperature).
Heretofore, multiblock copolymers have been used in a sprayable hot melt pressure-sensitive adhesive formulation with limited success. Such multiblock copolymers include, for example, poly(styrene-isoprene-styrene) ("SIS"), poly(styrene-butadiene-styrene) ("SBS"), poly(styrene-ethylene/butene-1-styrene) ("SEBS") and the like. Other two-phase polymers such as ethylene-vinyl acetate copolymer (EVA) have also been used. The multiblock copolymers (SIS, SBS and SEBS) are usually formulated with tackifiers and oils to form HMPSA's, whereas EVA's are generally formulated with tackifiers and wax for HMA's. The cohesive strength of these polymers depends strongly on the presence of a discrete, rigid reinforcing phase, e.g. polystyrene domains in the block copolymers and, in the case of EVA's, the crystallized phase of these semi-crystalline polymers.
The use of block copolymers in adhesive applications has grown rapidly in recent years. Their advantage over homopolymers or random copolymers such as natural rubber and styrene-butadiene rubber is shear performance and high temperature performance. This derives from the persistence of polystyrene phase structure in the tackified adhesive formulations. These high glass transition temperature (T.sub.g) domains function as physical cross-links, or fillers, which enhance modulus at high temperature and/or creep resistance over long periods of time. Therefore, an ideal tackifier would not intrude into the glassy polystyrene domains and should be either compatible, or at least partially compatible, with the elastomeric region of the two-phase polymers. Thus, different tackifiers are known to interact with block copolymers such as SIS, SBS and SEBS to affect viscoelasticity and adhesive performance.
A review on the melt rheology (i.e. at temperatures above T.sub.g of polystyrene) of styrene-diene triblock copolymers appears in Lyngaae-Jorgensen, in Processing Structure And Propertres Of Block Copolymers, ed. by M. J. Folkes, Elsevier, London, (1985). The rheological properties of a block copolymer with a two-phase structure involve gradual structural changes as a function of time and deformation. The nature of flow mechanisms and flow units (breakdown of phase morphology and type of steady state flow structure) presents both experimental and theoretical difficulties.
In Arnold et. al., Journal of Applied Polymer Science, vol. 14, p. 427 (1970), the structural breakdown of an SBS polymer in simple flow was described. At low frequencies, the polymeric melt is an essentially intact, three-dimensional network. As the frequencies increase to some intermediate values, the three-dimentional network transforms to a system consisting of large star-shaped aggregates. Domains still occur, now as the linking points of the large star-shaped aggregates. At sufficiently high frequencies, this aggregate is further disrupted to form a system of individual, nonaggregated molecules which flow similarly to an ordinary thermoplastic of the same molecular weight (that is, in a monomolecular melt state).
From U.S. Pat. No. 3,235,626 to Waack, it is known to use vinyl terminated macromonomers in forming graft copolymers. In this patent, a macromonomer is prepared by reacting a vinyl metal compound with an olefinic monomer to obtain a vinyl terminated macromonomer. After protonation and catalyst removal, the prepolymer is dissolved in an inert solvent with a polymerization catalyst and is subsequently reacted with either a different polymer having a reactive end group, or a different vinyl monomer under free radical conditions. This technique suffers from two major limitations: (1) though the use of vinyl lithium ensures that each polymer chain has one vinyl end group, vinyl lithium is one of the slowest anionic polymerization initiators, and results in a very broad molecular weight distribution wherein the ratio M.sub.w /M.sub.n is greater than 2, a consequence of the ratio of the overall rate of propagation of the styryl anion to that of the vinyl lithium initiation, with the result that graft copolymers prepared from these macromonomers cannot provide a uniform side chain molecular weight; and (2) substituted vinyl compounds do not generally polymerize to high conversions and the conversion decreases as the length of the side chain increases. Conversions of 50 percent, although relatively high for most substituted vinyls, means that the resulting graft copolymers contain 50 percent unreacted macromonomer which, for most applications, is unacceptable.
An alternative route, controlled termination of living polymers, is known from U.S. Pat. No. 3,989,768 to Milkovich et al., and Milkovich et al., J. Appl. Polym. Sci., vol. 27, p. 4773 (1982). These references describe anionic polymerization of a number of monomers of active initiators to form monodisperse living polymer chains. These living chains are then reacted with a wide range of termination agents to introduce substantially endfunctionalized macromonomers. Although this route clearly improves the resulting macromonomer polydispersity and allows for a broader range of endfunctionalities, it nonetheless introduces an uncertainty into the "purity" or "cleanness" of the end functional groups since one can no longer be assured that each and every chain has one functional group. Although each step in the preparation of such end-functionalized macromonomers can separately be about 95 percent in yield, the steps together produce a polymer that is, at best, only 80 to 90 percent end-functionalized.
The most informative characterization of graft copolymers produced using the Milkovich-type macromonomers comes from an analysis of the graft copolymers produced thereby. In Huang et al., J. Poly. Sci.: Part A: Polym. Chem. Ed., vol. 24, pp. 2853-2866 (1986), the vinyl terminated macromonomer described in Milkovich '768 was utilized to prepare graft copolymers of ethylene and propylene. The best conversions for vinyl terminated polystyrene macromonomers, with a moderate molecular weight and useful feed composition in the range of 10 to 30 weight percent, on ethylene-propylene copolymer was 40 percent.
In view of this prior art, it would be highly desirable to devise a means for preparing macromonomers wherein the guaranteed functionality introduced in the initiation step is combined with a more active polymerizable group.
The preparation and use of copolymers of styrene and isobutylene is known in the art. Thus, such copolymers ranging from tough, glassy high polystyrene content copolymers for use in plastic blends, to rubbery low styrene isobutylene copolymers for use as impact modifiers, etc., have become well known in this art. Styrene and isobutylene have been copolymerized rather readily in the past under cationic polymerization conditions to yield these copolymers covering the entire compositional range. It is also known that blocky or random homogeneous copolymers can be produced by altering the copolymerization conditions, such as shown in Powers, U.S. Pat. No. 3,948,868. This patent thus describes the production of random homogeneous polymers comprising at least two cationically polymerizable monomers such as isobutylene and styrene. This disclosure also includes a lengthy list of various olefinic compounds including isobutylene, styrene, .alpha.-methylstyrene and other such compounds. Furthermore, these compounds have been used in a variety of applications, including use as adhesives in connection with other materials taking advantage of the surface characteristics of the polyisobutylene sequences, as coatings, as asphalt blends, and in various plastic blends. As is discussed in the '868 patent, it is also well known to produce terpolymers including isoprene, but doing so reduces the overall polymer molecular weight rendering the production of high molecular weight polymers therefrom difficult, and complicating the overall production sequence.
There have also been attempts to produce various functionalized polymers. For example, Hankey et al., U.S. Pat. No. 3,145,187, discloses polymer blends which include a vinyl chloride polymer, a surfactant, and a chlorinated olefin polymer, and the latter is said by this patentee to include copolymers of various materials which can include isobutylene and styrene, as well as ring-alkyl styrenes, among a large number of other compounds, which olefin polymers can then be chlorinated by known methods.
The literature has also disclosed other routes for obtaining copolymers of isobutylene and styrene, such as that shown in Powers et al., U.S. Pat. No. 4,074,034, which discloses the copolymerization of isobutylene with halomethylstyrene. This technique requires the use of vinylbenzyl chloride and the like as starting material, and utilizes a specified continuous solution process with solvent or mixed solvent systems in which the monomers are soluble under specified conditions. Aside from the need to employ the expensive vinylbenzyl chloride starting material, these processes also have limitations in terms of the quantity of aromatic chloromethyl functionality which can be incorporated in this manner without encountering excessive chain branching and gel formation during polymerization and polymer recovery because of the reactivity of the benzylic chlorine under cationic polymerization conditions. See, "Isobutylene copolymers of vinylbenzyl chloride and isopropenylbenzyl chloride," Journal of Applied Polymer Science, vol. V, Issue No. 16, pp. 452-459 (1969) in which the aromatic monomer is said to be a mixture of the para and meta isomers.
There has also been some interest in the halomethylation of isobutylene/styrene copolymers, such as discussed in a paper by Sadykhov, et al. entitled "Chloromethylation of an Isobutylenestyrene Copolymer and Some of Its Chemical Reactions," Acerb. Neft. Khoz., 1979 (6) 37-9.
In an article by Harris, et al. entitled "Block and Graft Copolymers of Pivalolactone . . .", Macromolecules, 1986, vol. 19, pp. 2903-2908, the authors discuss the copolymerization of isobutylene with styrene and preferably a ring-methylated styrene. This article specifically discloses copolymerization with vinyl toluene, comprising a mixture of meta- and paramethylstyrene in approximately 65/35 amounts, and with para-methylstyrene, for the purpose of producing thermoplastic elastomer pivalolactone copolymer systems with no autooxidizable aliphatic unsaturation. The article fails to recognize any difference between the use of vinyl toluene and para-methylstyrene, and in any event, even when it employs the latter, it employs conditions which result in copolymers having the properties, including heterogeneous compositional distribution and very broad molecular weight distribution for the unfractionated copolymer, as set forth in Tables 4 and 5, which include an M.sub.n for the unfractionated copolymer of 16,000, and M.sub.w /M.sub.n of 17.45, and a 4-methylstyrene content in the polymer which varies considerably from the monomer feed and varies significantly as a function of molecular weight.
Finally, there are also articles which discuss copolymers of isobutylene and para-methylstyrene without discussing any method for preparing them. These articles include Sadykhov, et al., "Studies of Oxidative Thermal Degradation of Copolymers of Isobutylene with m- and p-Methylstyrenes in a Solution of Mineral Oils," Uch. Zap. Azerb. Un. t. Ser. Khum., 1975 (304), 87-92, and other such articles. Furthermore, in Toman, et al., "Isobutylene Polymers and Copolymers with Controlled Structure", App., 78/7, 339, (Nov. 10, 1978), there is reference to the copolymerization of isobutylene with vinyl aromatic monomers. The search has thus continued for useful molecular weight copolymers of isobutylene and alkyl styrenes, and in particular for functionalized copolymers of this type which can be crosslinked, and otherwise used in a variety of applications.
Polymers with a saturated hydrocarbon backbone are well known to possess good environmental and aging resistance which makes them highly desirable in a variety of applications. Furthermore, rubbery copolymers containing major amounts of polyisobutylene are well known to possess low permeability, unique damping properties, and low surface energy which makes them particularly highly desired in many applications. However, the "inertness" of these saturated hydrocarbon polymers, their low reactivity and incompatibility with most other materials, and the difficulties in adhering them to, or using them in conjunction with most other materials has restricted their use in many areas.
In commonly assigned U.S. patent application Ser. No. 441,575, filed Nov. 22, 1989, which is a Continuation-in-Part of copending U.S. patent application Ser. No. 416,503 filed Oct. 3, 1989, which is a Continuation-in-Part of copending U.S. patent application Ser. No. 199,665 filed May 27, 1988; and copending U.S. patent application Ser. No. 416,713 filed Oct. 3, 1989, which is a Continuation-in-Part of U.S. patent application Ser. No. 199,665 filed May 27, 1988; the disclosures of which are hereby incorporated by reference, it was theorized that the introduction of controlled amounts of the desired specific functionality as pendant groups on the saturated hydrocarbon backbone would greatly extend usefulness by permitting these polymers to be adhered to other surfaces and/or be co-reacted with or compatibilized with other functional polymers by "grafting" or crosslinking reactions. It was further theorized that the introduction of pendant functionality of the right type and amounts would permit these saturated hydrocarbon polymers to be "painted" or coated with other materials or to be used as a coating on other materials and/or to be laminated with or dispersed in other materials to yield composite materials with a desired combination of properties.
As has been already pointed out, the fact that benzylic halogen functionality constitutes a very active electrophile that can be converted to many other functionalities via S.sub.N 2 nucleophilic substitution reactions has long been recognized, and the chemical literature is replete with examples of these reactions. "Clean" conversions in high yield to many functionalities, including the following have been reported: aldehyde, carboxy, amide, ether, ester, thioester, thioether, alkoxy, cyanomethyl, hydroxymethyl, thiomethyl, aminomethyl, cationic ionomers (quaternary ammonium or phosphonium, S-isothiouronium, or sulfonium salts), anionic ionomers (sulfonate and carboxylate salts), etc. In addition, the literature described many examples in which a benzylic halogen is replaced by a cluster of other functionalities by nucleophilic substitution with a multifunctional nucleophile such as: triethanol amine, ethylene polyamines, malonates, etc.
Nearly all of this previous work has been with simple, small (i.e. non-polymeric) molecules containing the aromatic halomethyl (or benzylic) functionality. However, a considerable amount of art also exists on nucleophilic substitution reactions involving chloromethyl styrene and polystyrenes containing aromatic chloromethyl groups to introduce other functionalities. Much of this work involves reactions with "styragels" or lightly crosslinked polystyrenes containing various amounts of benzylic chlorine, and while many of the same nucleophilic substitution reactions previously reported for small molecules containing benzylic chlorine have been achieved in "styragels," it has been necessary to modify reaction conditions and in particular to often employ phase transfer catalysts in order to promote the desired substitution reaction. Reactions involving the benzylic chlorine in polystyrene have been more difficult to achieve than in simple small molecules because of the greater difficulty in achieving the intimate contact required between the reactants when one of the reactants (the aromatic chloromethyl moiety) is in a separate polymeric phase from the other reactant. Yields have also generally been lower and side reactions are more prevalent in the reactions involving the benzylic chlorine in polystyrene. However, since most of the work has been with "styragels," it has generally not been necessary to achieve high conversion in "clean" substitution reactions in order to preserve polymer solubility. Recent reviews of this work involving chloromethyl styrene and "styragels" containing benzylic chlorines are in the literature. See Marcel Camps et al., in "Chloromethylstyrene: Synthesis, Polymerization, Transformation, Applications" in Rev. Macromol. Chem. Physics, C22(3), 343-407 (1982-83) and JMJ Frechet in "Chemical Modification of Polymers via Phase Transfer Catalysts" in Crown Ethers and Phase Transfer Catalysts in Polymer Science, edited by Matthews and Canecher and Published by Plenum Press, NY, 1984, and Jean-Pierre Montheard, et al. in "Chemical Transformations of Chloromethylated Polystyrene" in JMS-Rev. Macromol. Chem. Phys., C-28 (3 & 4) pp. 503-592 (1988).
Previous workers have not applied nucleophilic substitution reactions to isobutylene/para-bromomethylstyrene/para-methylstyrene terpolymers to produce versatile, substantially saturated, macromonomer-grafted shear thinning copolymers.